Field of the Invention
The present invention relates to the field of display technology, and more particularly to a driving circuit for a display panel and a liquid crystal display device using the same.
Description of the Related Art
As a new generation display technology, Active Matrix Organic Light Emitting Diode (AMOLED) display panels have the advantages of low power consumption, a wide color gamut, high brightness, high resolution, etc., thereby being favored by the market. However, since the emission of AMOLED is driven with an electric current flowing from a transistor operated in saturation, the use of AMOLED has faced many problems including:
Organic light emitting diodes (OLED) have an aging problem. Since most of the conventional technologies use DC driving, holes and electrons are fixed in moving directions, they are respectively injected into an emission layer from an anode and cathode to form excitons through recombination, and eventually resulting in light emission. Redundant holes (or electrons) that were not involved in the recombination process may accumulate at a junction between a hole transport layer and the emission layer (or between the emission layer and an electron transport layer), or may pass through a potential energy barrier and then enter the electrodes. As the work time of the OLEDs extends, those un-recombined charge carriers which have accumulated at the junction will form a built-in electric field inside the OLEDs, and thereby result in a continuous increase in threshold voltage of each one of those light emitting diodes, thereby lowering their brightness, and also gradually reducing the energy utilization efficiency.
In a low-temperature poly-silicon (LTPS) technology, known as the mainstream manufacturing technology for OLEDs, there is a lack of uniformity in the threshold voltage of the transistors manufactured by the LTPS technology. Therefore, when the same gray-scale voltages are inputted to the transistors, different threshold voltages will generate different driving currents, and lead to inconsistency of electric current.
For example, with reference to FIG. 1, FIG. 1 shows a conventional 2T1C (two transistor, one capacitor) AMOLED driving circuit design, wherein member 11 is a thin-film transistor which is a scanning switch for controlling a capacitor 10; member 12 is an OLED driving transistor that is used to drive an OLED; the capacitor 10 is used to store the gray-scale voltage of a data signal, so as to control the driving current of transistor 12 to the OLED. In the circuit diagram, “Gate n” means the scanning signal from the n-th scanning line, “Data n” means the data signal from the n-th data line, and “Vdd” means the driving signal of the OLED. Due to the aforementioned aging problem of OLEDs and uniformity problems which occur in the LTPS manufacturing process, the threshold voltage Vth of the transistor in this conventional 2T1C driving circuit is shifted, thereby causing unstable gray-scale performance of the OLED and worse uniformity of the driven images.